1. Field of the Invention
The present invention relates generally to multifocal lens designs. More particularly, the present invention pertains to a method of designing and fitting multifocal lenses taking into account the material properties of the lenses.
2. Discussion of the Prior Art
The present invention pertains to ophthalmic lenses, and in particular to contact lenses such as soft hydrogel contact lenses, and intraocular lenses, having more than one optical power or focal length.
It is well known that as an individual ages, the eye is less able to accommodate. i.e., bend the natural lens in the eye in order to focus on objects that are relatively near to the observer. This condition is referred to as presbyopia, and presbyopes have in the past relied upon spectacles or other lenses having a number of different regions with different optical powers to which the wearer can shift his vision in order to find the appropriate optical power for the object or objects upon which the observer wishes to focus.
With spectacles, the process involves shifting one's field of vision from typically an upper lens portion far power to a lower lens portion near power. With soft or hydrogel contact lenses, however, this approach has been less than satisfactory. The contact lens, working in conjunction with the natural lens. forms an image on the retina of the eye by focusing light incident on each part of the cornea from different field angles onto each part of the retina in order to form an image. This is demonstrated by the fact that as the pupil contracts in response to brighter light, the image on the retina does not shrink, but rather, light comes through a smaller area of the lens to form the entire image.
Similarly, for a person that has had the natural lens of the eye removed because of a cataract condition and an intraocular lens inserted as a replacement, the ability to adjust the lens (accommodate) the distance of the object being viewed is totally absent. In this case, the lens provided is usually set at a single infinite distance focal power, and spectacles are worn to provide the additional positive optical power needed for in-focus closer vision. For such a patient, a functional multifocal lens would be particular useful.
It is also known in the art that under certain circumstances the brain can discriminate between separate competing images by accepting an in-focus image and rejecting an out-of-focus image.
U.S. Pat. No. 5,448,312 entitled PUPIL TUNED MULTIFOCAL OPHTHALMIC LENS, discloses a multifocal concentric ophthalmic lens for presbyopic patients constructed with three general annular lens portions in a multifocal design. A central circular portion of the lens has only the patient's distance corrective power, and is surrounded by a first inner annular portion, which can consist of multiple annular rings having an inner radial portion which enhances the patient's near focal power encircled by radial portions of substantially equal cumulative amounts of distance and near optical power focal correction for the patient. This is surrounded by a second outer annular portion, which can also consist of one or more annular rings having additional distance focal power near the periphery of the optical surface area of the ophthalmic lens. Each annular ring has either a near or distance optical power and works in combination with other lens portions to yield the desired focal ratio in that portion of the lens.
U.S. Pat. No. 5,485,228, entitled MULTIFOCAL OPHTHALMIC LENS PAIR, discloses a pair of ophthalmic lenses both containing at least two optical powers, one for near vision and one for distance vision. Both lenses, however, contain the distance power in the center portion of the lens. In one embodiment, the remainder of the lens includes annular portions, each made of one or more optical zones to provide the desired combined, cumulative ratio of near and distance focal length areas at each pupil diameter. In this way, the center portion of the vision contains a single optical power which results in improved visual acuity. This distance portion in the center is particularly well suited to the real world situation of requiring distance vision under high illumination situations.
The patents referred to above are hereby incorporated by reference in their entirety.
In prior art lens designs, no allowance is typically made in the lens design for individual fitting characteristics. As a result, whether or not a lens is successful depends on whether or not a proper fit is achieved. Because no allowance is made for individual fit, not all lenses are properly fitted.